> <i><font color="yellow">What do you think will be the reason for them remaining grounded? Debris/Frost/Slush?</font>/i><br /><br />Cracks in landing gear. More failed sensors. Another problem with ISS forcing the crew to abandon it (this seems to be an on-going issue: another problem with an oxygen candle, loss of a Russian resupply rocket, etc.). There are lots of possibilities.<br /><br />But here is a thought from left field: NASA completely changes course.<br /><br />The initial assessment from the Exploration Systems Architecture Study (ESAS) is due by mid-July
link -- before the next shuttle launch (?). While very unlikely I could see them drawing the following conclusions:<br /><br />"<i>ISS cannot be completed as planned by the retirement of the shuttle, and the ongoing $4 billion per year operational costs of the shuttle prevent new technologies from being developed. Therefore we recommend that the shuttle fleet be grounded immediately and the $4 billion be used to accelerate a shuttle-derived HLV, a crew transfer vehichle (CXV), and a Crew Exploration Vehicle to move humans and supplies between LEO and the Lunar surface. The Shuttle-derived HLV and CXV can be used to complete and support the ISS, and they have direct application to fulfulling the Vision for Space Exploration (VSE). Without freeing up the $4 billion per year from Shuttle operations, there is no reasonable expectation that significant advancement can be achieved on the VSE before NASA loses the support of Congress and the public and the VSE is canceled.</i>"</i>